The invention relates to a method for controlling a quantity of ink located on an ink roller of a printing machine during the processing of a printing job. The larger this ink quantity is, the more intense the tinting or coloration thereof is. It is therefore important to keep this ink quantity constant as long as the print result is satisfactory with respect to the tinting or color thereof, and to be able to adjust the ink quantity to a new value as quickly as possible, if color deviations are discovered, it being expected that the new value would be able to deliver a satisfactory inked printing result.
The inking unit of a printing machine typically includes an ink source, potentially in the form of an ink fountain or duct having a metering device, and a transport device, which includes a greater or lesser number of ink rollers and which feeds the ink quantity flow that is apportioned by the ink source to the printing form. Printing machines for high-quality ink printing allow an independent control of such an ink roller, respectively, zonally. Printing machines with this characteristic are described in the published German Patent Documents DE 40 04 056 A1, DE 37 07 685 A1 and DE 197 27 387 C1, for example. In this way, zones of the ink roller that serve for inking zones of the printing form having a high ink consumption are inked more intensely than those zones having a low consumption. In order to set the ink quantity on a zone of the ink roller to a new value, it is necessary to vary the ink quantity flow that is released for this zone from the ink source. Because this ink quantity flow is distributed to a large number of rollers before reaching the printing form, a fairly long time passes between a modification of the desired or nominal value of the ink quantity and a corresponding resetting of the metering device, on one hand, and the time at which the modified proportion influences the quantity of ink on the roller and thus the ink supply to the printing form. During this time, spoilage is produced.
It is therefore highly desirable to keep this time as short as possible. To this end, applicants have developed a method by which, when the desired or nominal value of the ink quantity for a zone of the roller is changed from a first value to a second value, a first correction ink quantity flow is prescribed, and during a transition interval, the ink quantity flow for this zone is set to the sum of the correction ink quantity flow and the ink quantity flow corresponding to the second desired or nominal value. When the second desired or nominal value is greater than the first, the correction ink quantity flow is positive, and when the second desired or nominal value is less than the first, the correction ink quantity flow is negative. This means that ink which is sufficient for a time, i.e., too little ink, is fed from the ink source, in order to obtain the desired or nominal quantity of ink on the ink roller as rapidly as possible, and after the expiration of a time-span after which this second ink quantity should have been approximately attained, there is a changeover to the ink quantity flow corresponding to the second ink value, which is dimensioned so that the second ink quantity is maintained on the roller in continuous operation.
This method has been used in the inking units of Heidelberger Druckmaschinen A.G. of Heidelberg, Germany since 1986. A corresponding method is also described in the published German Patent Document DE 43 37 343 A1. The application of similar methods for dampener control in an offset printing machine has become known heretofore from the published German Patent Documents DE 39 07 584 A1 and DE 197 01 219 A1.
A problem arises in the control of the ink quantity zonally in that when the desired or nominal value of the ink quantity flow that is released by the ink source for one zone is changed, not only the ink supply of the corresponding zone of the printing form is changed, but also that of neighboring zones. The reason for this is that the ink in the inking unit of the printing machine is distributed, so that an exchange of ink takes place between different zones.
The ink exchange between the zones prolongs the time until a steady state sets in again in the affected zone and the neighboring zone subsequent to modification of a desired or nominal value.
Another problem of the conventional ink quantity regulation by a correction ink quantity flow is that, for a sharp reduction of the desired or nominal value of the ink quantity, the correction ink quantity flow is so intensely negative that the sum of the correction ink quantity flow and the ink quantity flow corresponding to the second desired or nominal value, a sum which must be set during the transition time interval, is less than zero. Such a negative ink quantity flow would correspond to the uptake of ink from the inking unit by the ink source and cannot be realized using conventional ink sources. It therefore takes a particularly long time before a new desired or nominal value for the ink quantity of a zone actually to be attained in this case.
A similar problem arises when the desired or nominal value of the ink quantity is increased. The greatest possible ink quantity flow that the ink source can apportion in one zone is limited, and it is conceivable that when the desired or nominal value of the ink quantity flow is increased, the sum of the correction ink quantity flow and the ink quantity flow corresponding to the second desired or nominal value, a sum which is set during the transition interval, is greater than the maximum quantity of ink that can be apportioned. In this case, as well, the new desired or nominal ink quantity is attained only with a considerable delay.
It is accordingly an object of the invention to provide a method for controlling ink quantity in different zones of an ink roller which allows a rapid setting of a new desired or nominal value of the ink quantity even in the foregoing cases; is i.e., a method by which a zone for which the desired or nominal value of the ink quantity has been changed and the neighboring zones thereof attain stationary ink quantities as rapidly as possible.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for controlling an ink quantity in different zones of an ink roller in a printing machine, nominal values of the ink quantity for each zone being prescribed in a time-dependent manner, and a value of the ink quantity flow released for the zone by an ink source corresponding to each nominal value of the ink quantity, whereby, when the nominal value for the zone remains constant, a constant ink quantity is maintained in the respective zone by a release from the ink source of an ink quantity flow corresponding to the nominal value, and in the event the nominal value for a given zone is changed from a first value to a second value, the ink quantity in the given zone is changed in that a first correction ink quantity flow is prescribed in accordance with a given rule dependent upon the first and the second nominal values and, during a transition interval, the ink quantity flow for the given zone is set to the sum of the first correction ink quantity flow and the ink quantity flow corresponding to the second nominal value, which comprises prescribing additional correction ink quantity flows for the zones situated adjacent the given zone and, during the transition interval, setting the ink quantity flow for each of the zones situated adjacent the given zone to the sum of the correction ink quantity flow and the ink quantity flow corresponding to the nominal value of the given zone.
In accordance with another mode, the method includes imposing a condition for prescribing the additional correction ink quantity flows that the difference between the first and the second nominal values exceeds a limit value.
In accordance with a further mode, the method includes imposing a condition for prescribing the additional correction ink quantity flows that the sum of the correction ink quantity flow and the ink quantity flow for the given zone, which corresponds to the second nominal value, is outside of a limit value.
In accordance with an added mode, the method includes imposing a condition for prescribing the additional correction ink quantity flows that the sum of the correction ink quantity flow and the ink quantity flow for the given zone, which corresponds to the second nominal value, exceeds an upper limit value.
In accordance with an additional mode, the method includes imposing a condition for prescribing the additional correction ink quantity flows that the sum of the correction ink quantity flow and the ink quantity flow for the given zone, which corresponds to the second nominal value, falls short of a lower limit value.
In accordance with yet another mode of the method invention, the lower limit value for the ink quantity flow is when the ink zones are closed.
In accordance with yet a further mode of the method invention, the upper limit is the maximum ink quantity meterable for the given zone from the ink source.
In accordance with yet an added mode of the method invention, the correction ink quantity flows, respectively, are constant in the transition interval.
In accordance with yet an additional mode, the method includes providing that the ratio of the additional correction ink quantity flows to the first correction ink quantity flow is defined to be greater, the more intense the lateral distribution or rubbing of the ink in the printing machine is.
In accordance with a concomitant mode, the method includes providing that the ratio of the additional correction ink quantity flows to the first correction ink quantity flow is defined to be greater, the smaller the area covered by the zones which are allocated to the correction ink quantity flows.
The additional correction ink quantity flows expediently have the same operational sign and a smaller absolute value than the first correction ink quantity flow. The ratio of the ink quantity flows is advantageously defined in dependence upon the intensity of the distribution or rubbing of the ink in the inking unit; and namely, this ratio is larger, the more intense the distribution or rubbing is, and the smaller the area covered, i.e., the more intense the ink exchange between zones is.
In order to keep the control of the method simple, it can be provided, as a condition of prescribing the additional correction ink quantity flows, that the difference between the first and second desired or nominal values exceeds a limit value. The underlying idea of this is that when the difference in desired values is small, the ink modification in the affected zone is small, and consequent changes in the ink quantities in neighboring zones will barely be perceptible and will not have any noticeable influence on the printing results.
Alternatively or in addition, it can be provided, as a condition of prescribing the additional correction ink quantity flows, that the sum of the first correction ink quantity flow and the ink quantity flow corresponding to the second desired or nominal value for the given zone exceeds an upper limit value or falls short of a lower limit value. The lower limit can be zero, and the upper limit can be the maximum ink quantity flow that can be apportioned or metered for the given zone from the ink source.
A simple control is also achieved in that the correction ink quantity flows are each constant during the transition interval. The duration of the transition interval can be defined at a fixed value, particularly a value that is independent of the first and second desired or nominal values of the ink quantity.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as a method for controlling a quantity of ink in a printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.